1. Field of the Invention
This invention relates to seat belt systems employing seat belt retractors.
2. Description of the Prior Art
One type of seat belt system that has been extensively utilized is a system which includes a single emergency locking retractor which is mounted to the frame of a vehicle, such as on the "B" pillar. A single length of webbing may extend from the retractor in a continuous loop in order to provide lap and shoulder length portions. Another type of system that has been proposed especially with passive seat belt systems is one in which a retractor is mounted to the vehicle frame, such as the floor, inboard of the vehicle seat. During a collision, in such systems the force of the occupant moving against the belts is transferred to and absorbed by the vehicle frame via the retractor and/or buckle mountings. One problem with such systems is that considerable friction is typically experienced in the seat belt webbing extending over a variety of brackets which results in a larger force that is necessary to extend the webbing about the occupant as well as necessitating a stronger rewind spring to completely wind up the webbing.
It has been proposed to mount seat belt retractors directly onto vehicle seats, especially in passive seat belt systems, to provide for reduced friction in the system. Since the seats are adjustable, various means have been suggested to transfer the forces acting on the retractor in an accident to the vehicle frame. Such means should be flexible and adjustable to provide for different positions of the seat. It has been found, however, that even with such load transfer means, emergency locking seat belt retractors mounted on the vehicle seats may pay out excessive amounts of webbing in an impact situation, even though the retractor shaft is locked against rotation in the extraction direction, due to the so called spooling effect. That is, as the occupant exerts force against the webbing, the convolutions of webbing on the retractor spool tighten up and therefore make available an additional amount of webbing for further extraction prior to arresting further forward motion of the occupant. This spooling effect is also experienced with active seat belt systems but is more pronounced with passive seat belt systems since considerably more webbing is wrapped on the retractor spool when the belts are positioned about the occupant than in an active system.
It would be desirable if a seat belt system were provided which effectively transferred impact loads to the vehicle structure with limited spooling of the webbing on the retractor.